This invention relates to a pulp refining disk and method of making same. It relates more particularly to a disk of this type comprising an annular base supporting a circular array of spaced-apart knife blades projecting from the base.
Vegetable pulp used in the manufacture of paper, cardboard and the like materials is often refined by means of rotating refining disks. These disks consist of an annular base and a circular array of spaced-apart knife blades projecting from the base. When the rotating disks are emersed in the pulp, the pulp fibers are cut or reduced to a greater or lesser extent. The desired degree of reduction depends upon the type or function of the paper being made from the pulp. This desired reduction is achieved by controlling the number of disks, the number of knife blades on the disks and the height and thickness of the blades.
The degree of hardness of the knife blades used in such disks must be fairly carefully controlled. If the blades are too hard, they tend to be breakable so that the refining disks have a relatively short useful life. On the other hand, if the knife blade hardness is too low, the blades tend to lose their temper under the heat generated due to the friction between the rotating disk and pulp. This also shortens the life of the disk.
Therefore, with this in mind, it becomes important to consider the means employed to attach the knife blades to the disk face. One refining disk presently in use comprises an annular base made of steel with a circular array of knife blades welded into the surface of the base. Besides being expensive, this type of pulp refining disk is relatively inefficient because in the course of welding the blades to the disk, the heat generated during the welding operation deforms the disk and also causes the blades to use their temper or hardness.
Other conventional pulp refining disks are made by a casting process in which a steel base is cast onto the backs of the blades arranged in a circular array. Here again, the heat developed during the casting operation adversely affects the hardness of the blades and places limits on the height and thickness of the blades. This, in turn, adversely affects the efficiency of the disks in reducing the pulp fibers. This method of making the disks is also relatively expensive.